California hiking trails and campgrounds close to where British software developer, wife, baby and dog were mysteriously found dead are closed due to 'unknown hazards'

Federal officials closed trails and campgrounds in California's Sierra National Forest, citing the presence of 'unknown hazards', near the area where a British software developer and his family, including a dog, were found dead under mysterious circumstances last month.

'As a precaution and to protect the public from unknown hazards in the area, The SNF decided to close several recreation sites, roads, and trails along the Merced River and its South Fork, until deemed safe for public use,' the Sierra National Forest announced in a press release on Saturday. 

Officials revealed that the closures of more than a dozen picnic areas, campgrounds and forest trails, effective from August 29 through September 29, are due to 'unknown hazards found in and around the Savage Lundy Trail.'

The Sierra National Forest in California closed more than a dozen trails, campgrounds and picnic areas, citing 'unknown hazards' 

The closures that were announced on Saturday are in and around the area where Jonathan Gerrish, wife Ellen Chung, their baby daughter, Muji, and their dog were found dead in August

Forest officials closed recreational areas effective August 29 through September 26

On August 17, search and rescue teams discovered the bodies of Jonathan Gerrish, 45, his wife, Ellen Chung, 30, their one-year-old daughter, Muji, and the family dog, Oksi, on the Savage Lundy Trail. 

The notice announcing the closures stresses that signs warning the public of 'potentially harmful algae blooms' have been posted in the area sine mid-July. 

On Monday, the US Forest Service closed all forests in California through September 17 because of raging wildfires, including the Dixie, the second-largest wildfire in state history.    

Two weeks after the grim discoveries of the family's bodies in the remote part of Mariposa County, investigators still do not know how they died. 

According to the latest update from the Mariposa County Sheriff's Office, based on autopsies and a necropsy performed on the parents, child and their dog, officials have ruled out as causes of death gunshot wounds or injuries inflicted by any other type of weapon, as well as chemical hazards, such as gasses from an old mine along the Savage Lundy Trial. 

The bodies of the family of three and their pet were found on the Savage Lundy Trail, 1.5 miles from their parked truck  

There have been signs posted in the area since mid-July warning the public of toxic algae blooms 

Authorities are still awaiting toxicology reports and cell phone data before making any determination on how the family died.

Additional testing is also being performed by the CDC and Office of Environmental Health Hazards Assessment on water samples taken from the area and the drinking water the family had with them at the time of their deaths.

'We know the family and friends of John and Ellen are desperate for answers, our team of Detectives are working round the clock,' Mariposa County Sheriff Jeremy Briese said in a statement last week. 'Cases like this require us to be methodical and thorough while also reaching out to every resource we can find to help us bring those answers to them as quickly as we can.' 

Investigators revealed for the first time that Gerrish was researching the Hites Cove hike on a phone app the day before the family set off.

Two weeks later, investigators still do not know how the family died. Toxicology results are pending after gunshot wounds and injuries from other weapons have been ruled out 

At around 7.45am on August 15, a witness saw the family heading to the trail in their truck.

Detectives believe they managed most of a challenging 8.5-mile loop, which included 5 miles along a steep slope with little shade as temperatures reached 109 degrees, before they died on the hiking trail, about 1.5 miles away from their truck, which was parked at the Hites Cove trailhead. 

Oksi, the family's 9-year-old Akita mix, was found dead alongside his owners

A missing person's report was made at 11pm on August 16 and a Mariposa County sheriff's deputy discovered their truck at the end of Hites Cove Road at the trailhead around three hours later.

Search teams were deployed on the steep trails and the family were found along the switchbacks leading back to their trucks at 11am on August 17.

There were few clues for detectives at the scene and no signs of foul play, such as trauma, the police said.

No significant evidence was found in searches of the family home and vehicles, the sheriff's office said. FBI agents are currently working to extract data from Gerrish and Chung's phones. 

They were found on the Savage-Lundy hiking trail near Hites Cove, which was once a thriving mining community after gold was discovered in 1861. 

Gerrish was a software developer for Snapchat, had previously worked for Google. He graduated from Newcastle University. 

His American wife was studying psychology and the couple were very active and often spent time outdoors or traveling. 

WHAT ARE THE RISKS OF ALGAE BLOOMS? 

Cyanobacteria, also known as blue-green algae, are an ancient class of organisms that create the blooms are present nearly everywhere water is found, but thrive in warm, still bodies like lakes and ponds.

It includes species which produce some of the most powerful toxins known to man, and their impact on humans is only partially understood. 

The incidence of freshwater harmful algal blooms has surged in recent years, with some scientists attributing the increase to climate change. 

Algae is capable of producing several different toxins. People may be exposed to these toxins through contact with the skin (e.g. when swimming), through inhalation (e.g. when motor boating or water skiing), or by swallowing contaminated water.

These toxins can cause skin rashes, nausea, vomiting, stomach pains, fever and headaches.

Occasionally, the toxins can cause more serious illness such as liver and brain damage.

Children are at greater risk than adults of developing problems because of their comparative lower body weight.

The California Department of Public Health says it does not know of any human deaths from 'recreational or drinking water exposure to cyanobacterial toxin' although some animals have been killed by algae. 

Not all blue-green algae blooms and scums are toxic but it is not possible to tell from appearance and so it’s best to assume they are harmful and take the following precautions:

Anyone who has come into contact with water containing algae should shower with fresh water immediately.

Anyone who has come into contact with affected water and has become ill should obtain medical attention.